Rare earth-iron-boron based magnets, such as the well known Nd--Fe--B magnets, are used in numerous applications, including computer hardware, automobiles, consumer electronics and household appliances. In particular, magnets using rare earth elements, such as Nd or Pr, are useful primarily because of their superior magnetic properties, as manifested by their large coercivity, remanence, magnetization, and maximum energy product. The primary disadvantage of such magnets is that because of the cost of scarce rare earth metals, such as Nd or Pr, they are relatively expensive to make.
There are several known methods to fabricate rare earth-iron-boron magnets. In such methods, the constituent metals are melted together and subsequently solidified. Solidification is achieved by different techniques which include cooling, melt spinning, and annealing. The solidified alloy may take the form of an ingot, ribbon, flakes, or powder. Methods for fabricating magnets include sintering, hot pressing, hot deformation, and bonding. The process for making a sintered permanent rare earth magnet is well known and is described in, for example, U.S. Pat. Nos. 4,770,723, 4,792,368 and 5,645,651, which are incorporated herein by reference. The processes for making a hot-pressed or hot-deformed magnet are also well known and are described in, for example, U.S. Pat. Nos. 4,792,367 and 4,844,754, where are incorporated herein by reference. The process for making a bonded magnet is well known and is described in, for example, U.S. Pat. No. 4,902,361, which is incorporated herein by reference.
The oxygen content of the alloy or magnet affects its magnetic properties. A high oxygen content in the alloy causes a decline in the coercivity of the permanent magnet, preventing it from obtaining a high energy product. It is therefore desirable to have a process by which rare earth-iron-boron alloys and magnets are produced which limits their oxygen content. It is also desirable to have a process by which the metal yield from rare earth-iron-boron alloys is improved without adversely affecting the magnetic properties of the powder or magnet that may be formed.